In Reply:

Dr. Brown et al. have made important comments and raised good questions about the definition of intrinsic surgical risk and categorization of the different surgical procedures. We would like to take the opportunity to answer the questions and clarify intrinsic surgical risk stratification.

This study is an initial step toward risk stratification in patients under noncardiac surgeries, focusing on mortality.1  We would like to emphasize that the intrinsic surgical risk is the risk of 30-day mortality. It does not reflect the risk of morbidity including blood loss, possible postoperative mechanical ventilation, or unanticipated escalation of care and intensive care unit admission. For example, while patients undergoing craniosynostosis surgery may be considered at high risk for morbidity, the risk of mortality is low to nonexistent. In fact, a recent multicenter study by the pediatric craniofacial collaborative group reported a 15% complication rate.2  Despite this relatively high complication rate, there was no in-hospital mortality for patients undergoing cranial vault reconstruction surgery. This supports our categorization of craniosynostosis surgery as a procedure with a low intrinsic surgical risk of mortality.

The authors also raise a concern regarding the broad grouping of different procedures into the same risk category and the separation of similar procedures. When surgical procedures are identified by specialty, the relationship between mortality and a specific procedure is not possible. In fact, a recent study in adults examining intrinsic surgical risk of cardiac adverse events after surgery classified surgeries into three categories independent of anatomical location or surgical specialty.3  As an example, the study demonstrated wide variation in the intrinsic risk of individual procedures included under thoracic surgery as a specialty with a median odds ratio of cardiac risk of 1.40 and an interquartile range 0.88 to 2.17. This wide variation justifies the categorization of individual procedures based on individual common procedural terminology codes rather than anatomic location or surgical specialty.

The authors raised the question as to whether the risk quartiles are reflective of the emergent circumstances of the procedure. Intrinsic to some procedures, such as burr hole and laparoscopic appendectomy, are their emergent nature. The intrinsic surgical risk includes characteristics that are intrinsic to the need for a particular surgical procedure obviating the need for further adjustment. Nonetheless, to address the authors’ query, we calculated the odds ratios of the risk quartiles adjusting for case type (emergency or elective) using the 2012 to 2016 Pediatric databases of the American College of Surgeons National Surgical Quality Improvement Program, which was used to develop our model. Compared to risk quartile 2, risk quartile 3 has an adjusted odds ratio of 4.72 (95% CI, 3.14 to 7.10; P < 0.001), and risk quartile 4 has an adjusted odds ratio of 7.98 (95% CI, 5.27 to 12.07; P < 0.001). Independent of case type being an elective or emergency procedure, the intrinsic surgical risk quartiles continue to hold and are significantly associated with an increased risk of 30-day mortality.

Competing Interests

The authors declare no competing interests.

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